It is common for the key to get stuck in Murano when the battery is weak (or due to some other electric current interruption like bad ground), as the ignition switch needs current to operate. Try jump starting the vehicle, if jump start fails, check volts on the battery with a multimeter, it should be more than 12.2 volts, ideally at 12.6 volts. Check ground connections for corrosion, check battery connections, check connections in the fuse box for corrosion.